Chapter 4 Notes

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Published on 12 May 2011
School
UTSC
Department
Psychology
Course
PSYB51H3
Chapter 4: Perceiving and Recognizing Objects
-e.g. a house, simple cortical cells only see high contrast lines
-only sees parts, dont actually see house. Just lines.
-Middle (Midlevel) vision: Stage in seeing, after basic features are interpreted (early
vision). But before object recognition and scene understanding.
-combines features into objects
-e.g. how we a snowmans edges dont belong to the house
-recognition must involve matching what we see to memory
Middle Vision
-goal is to sort elements in scene into groups that we see as objects
Finding Edges
-cant assume lines that touch each other are objects b/c they overlap
-we fill in edges even when colours may be the same and there are gaps
-b/c of random in lighting
-illusory contour: When we see edges that arent actually connected
-e.g. fig. 4.5
RULES THAT MAKE CONTOURS
-structuralism: Complex perception can be understood by analyzing components
-i.e. perceptions are made of atoms from sensation (colour, orientation)
-see perception as built up from local sensations of atoms
-illusory contour disproves b/c gaps (cant have atoms) can be seen as having edges
-Gestalt: Whole is > sum of sensory parts
-german means form, everything has form, but we cannot always see it
-Gestalt grouping rules: rules for which elements are grouped from raw retinal image
-lines of sim. Orientation are seen as part of same contour
-parallel lines with gap btw support each other, make it easier to see lines between
them-e.g. fig 4.6
-even more so if the lines form a closed shape
-good continuation: gestalt grouping rule, elements group together if they seem to lie on
same contour
-e.g. fig 4.7
-we see lines that continue in one direction
-group edges that have seem orientation
PERCEPTUAL COMMITTEES
-perception is like committee, we take different rules, principles and guesses and come to a
consensus
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-one make overtake another, e.g. colour tells us contour as opposed to good continuation
OCCLUSION
-visual system wonders why an edge stops
-it may guess that something is blocking it
-when we combine this with good continuation, we get the illusory contour
Texture Segmentation and Grouping
-edge finding isnt very useful for texture differentiation
-texture differentiation: separating image into places with the same textures
e.g. fig 4.9 larger polygons are separated from smaller ones
-based on two principles:
Similarity: images that look the same are grouped together
e.g. similar colour, size, orientation and form
-combinations dont work well. i.e. difficult to tell diff between a combo of
features in image
Proximity: things that are closer are more likely to be grouped
-parallelism: parallel images likely grouped
-symmetry: symetrial images likely grouped
-common region: images likely grouped together if they look like part of a larger region
e.g. fig 4.12 line 2
-connectedness: images likely grouped together if they are connected
CAMOUFLAGE
-camouflage is getting features to group with environment when they shouldnt be
Perceptual Committees Revisited
-middle vision is like collection of specialists for different inputs from low level vision
-goal is to have single image out of these opinions
-committees are like connected neurons that take inputs and send them elsewhere to make
a image
COMMITTEE RULES: HONOUR PHYSICS AND AVOID ACCIDENTS
-decisions made by perceptual committees dont have to be final
-ambiguous feature: image that gives 2+ interpretations
-e.g. necker cube: cube that can be viewed in two ways fig 4.15
-accidental viewpoint: viewpoint that makes shapes look regular even though they
maybe oriented and placed differently
-e.g. fig 4.17
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Document Summary

E. g. a house, simple cortical cells only see high contrast lines. Middle (midlevel) vision: stage in seeing, after basic features are interpreted (early vision). E. g. how we a snowman"s edge"s don"t belong to the house. Recognition must involve matching what we see to memory. Goal is to sort elements in scene into groups that we see as objects. Can"t assume lines that touch each other are objects b/c they overlap. We fill in edges even when colours may be the same and there are gaps. Illusory contour: when we see edges that aren"t actually connected. Structuralism: complex perception can be understood by analyzing components. I. e. perceptions are made of atoms from sensation (colour, orientation) See perception as built up from local sensations of atoms. Illusory contour disproves b/c gaps (can"t have atoms) can be seen as having edges. Gestalt: whole is > sum of sensory parts. German means form, everything has form, but we cannot always see it.